Analysis of postural stability of the human body during the execution of standing industrial hand tasks

Abstract

Introduction: Foot positioning has a significant impact on human body stability control when completing a manufacturing task. In current Digital Human Models (DHM), the use of stepping strategies to generate stable postures relies on simplistic models, which generally locate the DHM center of mass (COM) at half distance between feet contact or limit the zero moment point (ZMP) projection within the base of support (BOS). Experimental data providing human movement coordination during manufacturing tasks, which can be used to simulate and validate these DHM models, are very scarce. Objective: The objective of this study is to develop an experimental test bench representing industrial conditions and to carry out experiments to provide these DHM models with parameters of postural stability. Material and Methods: A pilot subject performed four different one-handed standing working conditions namely: reaching a target, pushing and pulling a handle, as well as using a screwdriver. Each condition was performed in two different target positions. A transverse obstacle was used to impose spatial constraints for one of the target positions. The 3D kinematics of fifty reflective markers affixed on the anatomic human body with three additional markers on the screwdriver was recorded at 200 Hz using a motion capture system (VICON). Ground reaction forces and moments beneath each foot and at the targets was measured by three force plates (AMTI) simultaneously at 1000 Hz. The assessed postural stability parameters in this study were the support length which is a variation of the step length, and the ZMP position with respect to the BOS. Results: Experiments showed that task requirements vary the position and orientation of feet placement when an obstacle is present or not, which was consistent over all trials of moving the contralateral leg backward when the transverse obstacle was present. The mean support length magnitude appeared smaller for the handle location with a transverse offset which indicates hand-target reach might have been favored over stability. Conclusion: It is noted that the sample size is limited, hence the conclusions remain partial. In future works, it is intended to carry out the presented experimental protocol on a larger population size to develop a more precise regression model able of predicting the support length with respect to the ZMP position and its orientation about the target and the hand load direction requirements.

Date	7 Oct 2020
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Rachid Aissaoui (Supervisor) & Nicola Hagemeister (Co-supervisor)